The goal of this project is to utilize engineered forms of the enzyme cytochrome c peroxidase (CcP) to introduce an artificial electron pathway for rapid generation of redox intermediates. Part I of this proposal will evaluate the ability of a large range of substrates linked to Ru-photosensitizers by hydrocarbon tethers to bind to cavity mutants of CcP. This work will be expanded to include hydrocarbon tethers of various lengths. Part II involves the synthesis of short peptide tethers as linkages between the ligands and Ru-photosensitizer. This is expected to increase the range of tether-protein interactions. In Part III, electron transfer properties will be investigated. Photo- excitation of the Ru-photosensitizer will result in electron transfer from the Ru center to the heme iron through the cavity- docked ligands via the hydrocarbon or peptide tethers. Analysis of transfer rates will allow the investigation of the physical pathway of electron transfer as a function of electronic coupling and intervening medium to allow further optimization of tethered photosensitizers.